Decoding Alan Turing

Alan Mathison Turing (1912-1954), computer pioneer and mathematician, is guaranteed cultural immortality due to the meme of the Turing Test. It is hardly outlandish now to imagine a computer with human-level language skills. It was 55 years ago, when Turing suggested it. World War II buffs recall Turing as the intellectual leader of a team of code breakers. He was also homosexual in orientation, which led to the persecution that triggered his suicide.

Turing perfectly fitted the stereotype of the thinker who lives out of phase with reality. Naïve and solitary, he had an abrupt manner, a penetrating laugh and a voice that often changed pitch. He often ran simultaneous experiments in logic, chemistry and electronics. Unlike most theoreticians, he liked tinkering and cobbled together many odd devices. He was also an Olympic-level marathoner, a first-class shot, a rugby forward and oarsman, which meant that he hardly fitted the popular conception of a “pansy”.

One difficulty in getting to grips with this fascinating personality is that the last 15 years of his life are obscured by the Official Secrets Act. When Andrew Hodges, a mathematical physicist and gay rights activist, wrote the first edition of this biography in 1983, he faced that problem. Declassification has allowed the addition of new detail in the centenary edition. Dr Hodges has incorporated the new material through an expanded foreword and footnoting rather than by rewriting text.

This has the virtue of retaining the 1980s flavour. The world was then a very different place. The Cold War was in full swing and personal computing in its youth. Homosexuality had only been partially decriminalised in the UK.

Turing came from upper-class Anglo-Indian stock. His father was an Indian Civil Service officer of the Madras Presidency. His maternal grandfather was an Indian Railways engineer. He was born in the UK and shunted into public school, meeting his parents only when pater had “home leave”.

His schoolwork was untidy and illegible. He reinvented new solutions to conventional textbook problems. He failed twice to win scholarships to his institution of choice, Trinity College, Cambridge, before entering King’s College.

At 24, he found an elegant solution to one of Hilbert’s “problems of the century”: was it possible in theory to solve all maths problems by mechanical processes? Turing conceptualised a theoretical machine, which could solve every problem capable of solution. He proved that there would always be problems that could not be solved. This seminal paper, “On Computable Numbers”, meant access to mavens like John Von Neumann and Alonzo Church, who invited him to Princeton. He later developed the idea of a universal machine into practical computing.

During World War II, the British recruited an unlikely bunch of dons and chess players, parked them on a rural estate, and asked them to break German codes, which were generated on a multi-rotor device called the Enigma. The boffins of the Government Code & Cipher School (GC&CS), Bletchley Park, used intuition, statistical analysis, guesswork and logic to crack the codes. Their skills saved many Atlantic convoys and also prevented Rommel from over-running North Africa.

Turing was nicknamed “prof” and the undisputed genius of GC&CS. His mechanical ability helped him construct “bombes”, devices that reverse-engineered Enigma. While at Bletchley, he was engaged to fellow code breaker and mathematician Joan Clarke before confessing his orientation and breaking it off.

After Pearl Harbor, he was asked to put US cryptoanalysis on a sound footing. In the US, he collaborated with Claude Shannon on a prototype voice-scrambler, “Delilah”. There is a year (1943-44) missing from the record, when he was on liaison. Given the connections to Von Neumann and security clearances stemming directly from Churchill and Roosevelt, anything, including connections to the Manhattan Project, is possible.

Tales of the “prof’s” eccentricities grew. He normally worked dressed in pyjamas and blazer. He was detained on a US trip because he forgot to carry identification. He buried silver bars around Bletchley Park and lost the map to his nest egg. He joined up for the Home Guard to practise his shooting and answered “No” on the form where it said “Do you understand that you are under Military law?”

After the war, he spearheaded the computer revolution. He invented the concept of programming. He was still involved in high-security work as Britain developed her atom bomb and cryptoanalysis gained even more in importance.

In 1951, he had a few sexual encounters with a 19-year-old working class boy, Arnold Murray, and his house was burgled by one of Murray’s pals. During investigations, the police learnt about the gay activity. Turing had never made a secret of his orientation and he was hardly the only gay don. But he had got caught.

He had to undergo a course of hormonal injections — a so-called experiment in “chemical castration”. He also came under relentless surveillance. Although he bore up with apparent good grace and continued with various lines of research, he was forced out of “sensitive” work. In June 1954, he ate a cyanide-laced apple.

It was all very pointless. In 2009, Gordon Brown issued a posthumous apology for the appalling treatment Turing received. This book presents a sympathetic portrait, though it would be stretching truth to say it makes much sense of the enigmatic space between his ears. It also provides comprehensible descriptions of some of his work. It’s well worth reading for the scientific details, as well as the sociological snapshot of the 1930-55 era as seen from the 1980s.